Configuration for optimumization of starter-generator design

ABSTRACT

A self-excited compound type DC starter-generator with automatic switching from long shunt excitation to short shunt excitation when the starter-generator changes its operation from that of a motor to that of a generator. A shunt field winding is connected by a pair of diodes to two different junctions on a serially connected armature winding and series field winding. The diodes have biases of opposite polarity applied that permit current flow through only one of the two diodes at a time. When the startergenerator changes from motor to generator operation the bias on the diodes is reversed causing current flow in the opposite diode.

United States Patent [72] Inventor Joseph D. 2,806,962 9/ l957 Quantz290/3l Cherry Hill, NJ. 2,926,295 2/1960 Allen 318/506 21 Appl. No.860,286 3,221,173 11/1965 Hoover 290/46 x (22] Filed Sept. 23,19693,398,344 8/1968 McCormick 313/426 X [45] Patented July 27, 197i 1 1 mM-MMMM izzzzzfiz s digi-aisrsxwe,

represented by the Secretary of the Navy [54] CONFIGURATION FOROFI'IMUMIZATION OF STARTER-GENERATOR DESIGN m C 3 in: g ABSTRACT: Aself-excited compound type DC starter- [52] US. Cl 290/46, generatorwith automatic switching from long shunt excitation 1 2. 5 1 5 to shortshunt excitation when the starter-generator changes [51] Int. Cl ..H02k23/52 its operation from that of a motor to that of a generator, A [50)0 Search 290/37, 38, shunt field winding is connected by a air of diodesto two dif. ferent junctions on a serially connected armature windingand 427 series field winding. The diodes have biases of oppositepolarity applied that permit current flow through only one of the [56]References two diodes at a time. When the starter-generator changes fromUNITED STATES P E motor to generator operation the bias on the diodes is707,230 8/1902 Henry 290/19 reversed causing current flow in theopposite diode.

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ENGINE STATEMENT OF GOVERNMENT INTEREST The invention described hereinmay be manufactured and used by or for the Government of the Unitedstates of America for governmental purposes without the payment of anyroyalties thereon or therefor.

BACKGROUND OF THE INVENTION This invention generally relates to DCstarter-generators and, more particularly, to a unique field excitationcircuit for such starter-generators as normally used in jet aircraft.

The starter-generator begins operation as a motor in order to start anaircraft engine. When the engine comes up to rated speed, it in turndrives the starter-generator, so that the starter-generator thenoperates as a generator. The optimum configuration for the armature andfield windings is not the same on starting as a motor as it is onrunning as a generator. The long shunt configuration with the shuntfield winding connected in parallel to the serially connected armatureand series field windings provides best starter breakaway torque SUMMARYOF THE INVENTION accordingly, it is a general purpose of the presentinvention to provide, a field circuit configuration optimum for startingas I a motor, and then automatically switching to another field circuitconfiguration optimum for running as a generator.

This is accomplished in the starter-generator by the anodes of twodiodes being connected to the shunt field winding and having the cathodeof one diode connected to one side of the series field winding and thecathode of the other diode connected to the other side of the seriesfield winding. Then, de pending upon the bias on each of the diodes, theshunt and series fields winding are connected in either the long shuntor the short shunt configuration.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic diagram of astarter-generator circuit according to the present invention;

FIG. 2 is a simplified schematic diagram of the startergenerator of FIG.1 operating as a motor in a start" mode; and

FIG. 3 is a simplified schematic diagram of the startergenerator of FIG.1 operating as a generator in a "run" mode.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing, astarter-generator 10 has an armature winding 11 mechanically coupled toan engine 13. A series field winding I7 is connected in series with thearmature 11 at a junction 18, lnterpole windings (now shown) if includedin a starter-generator would be connected in a conventional manner tothe series field winding. A voltage regulator 20 is connected in serieswith a shunt field winding 21 of the starter-generator 10 and thisseries connection is in turn connected so that there is a parallelcurrent path with either the armature winding 11 or the armature windingII in series with the series fielding winding 17. This current pathdepends on the biasing of two diodes 24 and 26 that have their anodesconnected to an electrical terminal of the shunt field winding 21opposite to the shunt,field winding terminal connected to the voltageregulator 20. The cathode of diode 26 is connected at junction 18 whichis located between the armature winding 11 and the series field winding17. The cathode of diode 24 is connected at a junction 19 to theopposite side of the series field winding 17 than the diode 26.

The input-output terminals of the starter-generator 10 are connectedthrough a starting switch 14 to a DC power supply and a load L. Thenegative side of the DC supply may be connected to ground although thisis not essential for operation.

Switch 14 may be of any conventional type for motor starting; however,an ON-OFF switch I4 is shown for simplicity, as the details of thestarting circuit itself are not part of this invention.

The load L receives its power from the DC supply until thestarter-generator starts operating as a generator and supplies the powerfor the load L.

Operation of the starter-generator 10 is initiated by the closure ofswitch 14. The current delivered by the DC supply is designated I,. Thiscurrent is divided into the three parallel branches l,,, I,,, and I Thecurrent i through windings 11 and I7 produces a potential across theseries field winding 17 and places junction 18 at a higher potentialthan junction 19.

The current I, flows through the series connection of the voltageregulator 20, the shunt field winding 21, and the diode 24. Since thediode 24 is forward biased, a low resistance path connects junction 25with junction 19. This places junction 25 at a potential nearly equal tothat of junction 19. Junction 18 on the other hand has a higherpotential than junction 19 due to the potential across the series fieldwinding 17. Therefore junction 18 has a higher potential than junction25, and this higher potential reverse biases diode 26 causing diode 26to block all currents.

The start operation is the long shunt configuration of FIG. 2. Diode 24appears as a zero-resistance conductor as it is in effect a shortcircuit, and the path from junction 25 to junction 18 is omitted asdiode 26 in effect operates as an open circuit.

It is at this time the starter-generator l0 behaves as a motor. Oncoming up to rated speed, the engine 13 then drives the armature 11 andthe starter-generator 10 commences operation as a generator.

The current supplied by the armature winding 11 in FIG. 1 is designatedI, and provides parallel branch currents I 1,. and I The current Irecharges the DC supply, and current I is fed to the load I... The twocurrents 1,, and I, recombine at junction 28 into the current I +l andfiow through series field winding I7 causing a potential across theseries field winding 17 in an opposite direction to that developedduring motor operation. This current reversal gives junction 19 a higherpotential than junction I8. Junction 25 being at a voltage similar tothat of junction I9 now forward biases diode 26 causing a low impedancepath through diode26 to junction 18. This brings junction 25 to apotential near that of junction 18 and reverse biases diode 24, blockingcurrent through this original current path. The current I, now flowsthrough voltage regulator 20, shunt field winding 21 and diode 26.

The simplified schematic diagram of this generator operation can be seenin FIG. 3. It will be noted that the windings of starter-generator 10are now in a short shunt exciter field configuration. This provides foroptimum performance during operation as a generator.

It is seen that by the use of two diodes the starter-generator on beingenergized and operating as a motor is provided with a long shunt exciterfield for maximum breakaway torque. Once the starter-generator hasstarted the engine and is in turn driven by the engine, thestarter-generator operates as a generator and has the diodes convert theexciter field to a short shunt configuration for best overloadcharacteristics.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What I claim is:

l. A DC machine comprising:

an armature winding adapted to operate as a motor or generator;

a series field winding having one terminal thereof operatively connectedto one terminal of said armature winding;

a shunt field winding having one terminal thereof operatively connectedto the other terminal of said armature windcontrol means operativelyconnected to the other terminal of said shunt field winding and bothterminals of said series field winding responsive to the direction ofcurrent through said series field winding for automatically establishingalternative electrical conductivity between said other terminal of saidshunt field winding and wither terminal of said series field winding;and

a pair of input-output terminals operatively connected across said otherterminals of said series field winding and said armature winding andadapted to be simultaneously connected to a power supply and anelectrical load.

2. A DC machine according to claim 1 wherein said control means furthercomprises: I

a first diode operatively connected in series with said shunt fieldwinding across said armature winding only; and

a second diode operatively connected in series with said shunt windingacross both said armature and said series field windings.

3. A DC machine according to claim 2 wherein said first and seconddiodes have the anodes thereof connected in common.

4. A DC machine according to claim 3 further comprising:

a voltage regulator operatively connected in series with said shuntfield winding across said armature winding.

5. A power system comprising, in combination:

a power supply;

a load connected across said power supply;

an armature winding adapted to operate as a motor or generator andincluding a rotatable output shaft and one terminal operativelyconnected to one terminal of said power supply;

an engine drivingly connected to said output shaft;

a series field winding having one terminal thereof operative- -lyconnected to the other terminal of said armature winding and the otherterminal thereof connected to the other terminal of said power supply;

a shunt field winding having one terminal operatively connected to saidone terminal of said armature winding; and

control means operatively connected to the other terminal of said shuntfield winding and both terminals of said series field winding responsiveto the direction of current through said series field winding forautomatically establishing electrical conductivity between said otherterminal of said shunt field winding and said other terminal of saidseries field winding when said armature winding is operating as a motorand between said one terminal of said series fieldwinding when saidarmature winding is operating as a generator.

6. A power system according toclaim 5 wherein said control means furthercomprises:

a first diode operatively connected in series with said shunt fieldwinding across said armature winding only; and second diode operativelyconnected in series with said shunt winding across both said armaturewinding and said series field winding. I

7. A power system according to claim 6 wherein said first and seconddiodes have the anodes thereof connected in common.

8. A power system according to claim 7 further comprising:

a voltage regulator operatively connected in series with said shuntfield winding across said armature winding.

9. In A DC machine capable of starting as a motor and shifting into agenerator mode of operation wherein said DC machine having an armaturewinding in series with a series field winding and a shunt field windingin parallel across the series-connected armature and series fieldwinding, the improvement comprising: I I I I I a first diode connectedin series with said shunt field winding, the series combination of saidfirst diode and said shunt field winding being in parallel across saidseriesconnected armature and said series field winding; and

a second diode connected in series with said shunt field winding, andseries combination of said second diode and said shunt field windingbeing in parallel with said armature winding, said first and seconddiodes having the anodes thereof connected in common.

10. In a DC machine capable of starting as a motor and shifting into agenerator mode of operation wherein said DC machine having an armaturewinding in series with a series field winding and a shunt field windingin parallel across the series-connected armature and series fieldwinding, the improvement comprising:

a first diode connected in series with said shunt field winding, theseries combination of said first diode and said shunt field windingbeing in parallel across said series connected armature and said seriesfield winding; and

a second diode connected in series with said shunt field winding, theseries combination of said second diode and said shunt field windingbeing in parallel with said armature winding, said first and seconddiodes having common polarity electrodes joined together.

1. A DC machine comprising: an armature winding adapted to operate as amotor or generator; a series field winding having one terminal thereofoperatively connected to one terminal of said armature winding; a shuntfield winding having one terminal thereof operatively connected to theother terminal of said armature winding; control means operativelyconnected to the other terminal of said shunt field winding and bothterminals of said series field winding responsive to the direction ofcurrent through said series field winding for automatically establishingalternative electrical conductivity between said other terminal of saidshunt field winding and wither terminal of said series field winding;and a pair of input-output terminals operatively connected across saidother terminals of said series field winding and said armature windingand adapted to be simultaneously connected to a power supply and anelectrical load.
 2. A DC machine according to claim 1 wherein saidcontrol means further comprises: a first diode operatively connected inseries with said shunt field winding across said armature winding only;and a second diode operatively connected in series with said shuntwinding across both said armature and said series field windings.
 3. ADC machine according to claim 2 wherein said first and second diodeshave the anodes thereof connected in common.
 4. A DC machine accordingto claim 3 further comprising: a voltage regulator operatively connectedin series with said shunt field winding across said armature winding. 5.A power system comprising, in combination: a power supply; a loadconnected across said power supply; an armature winding adapted tooperate as a motor or generator and including a rotatable output shaftand one terminal operatively connected to one terminal of said powersupply; an engine drivingly connected to said output shaft; a seriesfield winding having one terminal thereof operatively connected to theother terminal of said armature winding and the other terminal thereofconnected to the other terminal of said power supply; a shunt fieldwinding having one terminal operatively connected to said one terminalof said armature winding; and control means operatively connected to theother terminal of said shunt field winding and both terminals of saidseries field winding responsive to the direction of current through saidseries field winding for automatically establishing electricalconductivity between said other terminal of said shunt field winding andsaid other terminal of said series field winding when said armaturewinding is operating as a motor and between said one terminal of saidseries field winding when said armature winding is operating as agenerator.
 6. A power system according to claim 5 wherein said controlmeans further comprises: a first diode operatively connected in serieswith said shunt field winding across said armature winding only; andsecond diode operatively connected in series with said shunt windingacross both said armature winding and said series field winding.
 7. Apower system according to claim 6 wherein said first and second diodeshave the anodes thereof connected in common.
 8. A power system accordingto claim 7 further comprising: a voltage regulator operatively connectedin series with said shunt field winding across said armature winding. 9.In A DC machine capable of starting as a motor and shifting into agenerator mode of operation wherein said DC machine having an armaturewinding in series with a series field winding and a shunt field windingin parallel across the series-connected armature and series fieldwinding, the improvement comprising: a first diode connected in serieswith said shunt field winding, the series combination of said firstdiode and said shunt field winding being in parallel across saidseries-connected armature and said series field winding; and a seconddiode connected in series with said shunt field winding, and seriescombination of said second diode and said shunt field winding being inparallel with said armature winding, said first and second diodes havingthe anodes thereof connected in common.
 10. In a DC machine capable ofstarting as a motor and shifting into a generator mode of operationwherein said DC machine having an armature winding in series with aseries field winding and a shunt field winding in parallel across theseries-connected armature and series field winding, the improvementcomprising: a first diode connected in series with said shunt fieldwinding, the series combination of said first diode and said shunt fieldwinding being in parallel across said series-connected armature and saidseries field winding; and a second diode connected in series with saidshunt field winding, the series combination of said second diode andsaid shunt field winding being in parallel with said armature winding,said first and second diodes having common polarity electrodes joinedtogether.